1. Field of the Invention
The present invention relates to a tape carrier (film carrier) and a tape carrier device mounted with an integrated circuit (IC).
2. Prior Art
As a conventional method of connecting an IC to a tape carrier to produce a semiconductor component for use in the tape automated bonding (TAB) method or the like, the following two methods are most popular.
One method comprises forming a device hole in an insulating film, having inner leads formed of a conductor such as mainly copper overhang in the device hole and then connecting the inner leads to Au metal bumps formed on IC chip electrodes by thermocompression bonding or the like. Alternatively, the bumps may beforehand be formed on the inner leads to bond the inner leads to the IC chip electrodes.
The other method comprises forming patterns on both surfaces of a tape carrier, forming electrode pads on one surface at positions corresponding to the electrodes of an IC chip, electrically connecting the electrode pads to wiring leads formed on the other surface through through-holes and then bonding the electrode pads on the tape carrier to the IC chip electrodes having solder bumps formed thereon.
Such a tape carrier is sealed with a sealing resin consisting of an epoxy-based resin or the like after bonding of IC to the carrier, and then the outer leads are bonded to another substrate by soldering, an anisotropic conductive film, a photo-curable insulating resin, or the like. To prevent formation of a solder bridge during soldering, to prevent pattern short-circuiting and corrosion caused by conductive foreign materials, to prevent reliability degradation caused by electromigration and formation of a whisker, to mask a portion free from plating for pattern finishing using Sn, Au or solder and to prevent outflow of the IC sealing resin to a portion connected to the substrate, an overcoat resin is generally applied, prior to IC bonding, to wiring patterns except for portions contributing to bonding.
As a conventional overcoat resin, an epoxy-based solder resist having a high strength of adhesion to an IC sealing epoxy-based resin, such as a CCR240GS (trade name) available from Asahi Kagaku Kenkyu-sho, has been used. In recent tape carriers having a high-density pattern, warping of tape carriers which is caused by a difference between the thermal shrinkage or expansion coefficients of the overcoat resin and an insulating polyimide film mainly causes a decrease in yield and reliability particularly during bonding of outer leads.
A conventional tape carrier coated with such an overcoat resin and a tape carrier device mounted with an IC thereon are shown in FIGS. 1(a) and 1(b), respectively. Referring to FIGS. 1(a) and 1(b), reference numeral 1 denotes a device hole; 2, an insulating film (tape); 3, a copper film pattern (The greater part of the pattern is coated with an overcoat resin 4 and, thus, only a non-coated portion is shown.); 4, an adhesive resin overcoat such as an epoxy resin-based one (epoxy-based solder resist); 5, outer leads; and 7, an IC sealing resin.
FIGS. 1(a) and 1(b) show a tape carrier and a tape carrier device for a liquid crystal driver. Inner leads overhanging in the device hole 1 are connected to an IC, and the connection portion and an IC circuit formation surface are covered mainly with an epoxy-based IC sealing resin. An epoxy resin-based overcoat 4 called a solder resist is applied to the wiring pattern formed on the tape carrier prior to IC connection. After the tape carrier device is confirmed to be a nondefective product by an electrical test after IC sealing, the outer leads 5 are bonded by an anisotropic conductive film or the like to an electrode pattern onto a glass substrate serving as a liquid crystal panel. At this time, the flatness of the outer leads portion of the tape carrier greatly influences workability and yields of the bonding step as well as reliability of the bonded portion. As described above, warping of the tape carrier will raise a serious problem when a conventional epoxy resin-based overcoat is attempted to be coated on the warped tape carrier.
FIG. 2 shows a conventional tape carrier different in type from that shown in FIG. 1(a). The same reference numerals in FIG. 2 as in FIG. 1(a) denote the same parts as in FIG. 2. Even the conventional tape carrier of the type shown in FIG. 2 is generally coated on its conventional pattern portion with an epoxy resin-based overcoat and, in this case, warping of the carrier tape will also pose a serious problem on forming and soldering the outer leads 5 to a substrate.
A recently developed polyimide resin-based overcoat such as an FS100 (trade name) available from Ube Industries, Ltd. has a remarkable effect to prevent warping of the tape carrier and, therefore, the problem posed by warping can be solved by the use of the polyimide resin-based overcoat. However, the strength of adhesion of the polyimide resin-based overcoat to an IC sealing resin is low, so that reliability of the tape carrier device to degrade is caused due to changes in temperature and humidity after mounting an IC on the tape carrier.